Telephone system.



PATENTBD APR. 80, 1907. J. W. LATTIG & O. L. GOODRUM.

TELEPHONE SYSTEM.

APPLICATION FILED APR. 4.1903.

13% 1' "use:

UNITED STATES PATENT @FFIUE.

JACOB W. LATTIG AND CHARLES LANE GOODRUM, OF PHILADELPHIA, PENNSYLVANIA.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented April 30, 1907.

Application filed April 4, 1903. Serial N0.151,1'79.

To all whom it may concern:

Be it known that we, JACOB l/VILLIAM. LAT- TIG and CHARLES LANE GOODRUM, citizens of the United States, residing in Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented a certain new and useful Improvement in Telephone Systems, of which the following is a specification.

Our invention relates to telephone exchange systems, and .has for its object the provision of improved signaling and testing means at the central office.

The invention is hereinafter described in connection with a common battery system forming-the subject of our patent granted March 10, 1903, No. 722,367.

In telephone exchange systems, even of small size, it is now customary to employ a centralized or common source of electrical energy, from which current is derived for use at the subscribers stations as well as at the central station. Such centralization of the power supply has rendered it possible to employ automatic signals throughout, that is, signals which do not require separate acts specially performed by subscriber or operator for their actuation or restoration to normal, but which respond directly to conditions as they are produced or changed in initiating, setting up, responding to, and terminating, a conversational connection. Thus, in modern systems a subscriber performs no special act in calling but simply removes his receiver from its hook and places it to his ear ready to converse and to listen, giving no thought to the signal, which nevertheless has responded to his closure of the line circuit. When the operator has set up the desired connection she need use no switch to ascertain the Wishes of the subscribers or the c011- dition of the lines, by listening or otherwise, for each cord circuit is provided with tell-tale signals (usually two in number, one for each subscriber) which respond faithfully to each change in condition of the line as it is affected by the use or disuse of the subscribers talking apparatus. Such systems are called supervisory systems, the automatic signals affording an opportunity for constant and perfect supervision simultaneously of all the connected lines controlled by each operator.

In most common battery systems the lines are normally extended when in disuse, to the main battery bus-bars through the windings of the line signal magnet or relay, and through the contacts of another relay, which is connected to contacts in the jack or jacks, to be energized when a plug is inserted therein, and thereupon cut off the extension of the line, whereby the line signal, being deprived of current, is restored to its normal condition. The cut-oif relay thus employed, requires a three conductor cord, but this disadvantage is considered preferable to cutting off in the jack, which is the alternative method. "0 employ neither method, but avoid the disadvantages of both by using shunts, closed when the plugs are inserted.

The feature to which we have referred is of course applicable to small systems, to trans fer systems, or to multiple-board systems; but in addition we have invented certain other features, cor'iperating with the above, and particularly applicable to multipleboards. One of these is a test, which we have shown as applied to a simple 1nultipleboard system, but which may also be applied to a multiple trunking system. In most systems a ground is required for test, and the test depends primarily upon changing the potential of the test rings when a plug is inserted in the ack. In many systems the circuits are complicated or the apparatus is complicated and unsuited to standardizing circuits for general use. 7e dispense with all complication, in the following manner: By connecting our supervisory relay to the sleeve side of the cord, and. the tip through the ordinary listening key, operators receiver, and high resistance choke coil to the negative side of battery, we complete a test circuit, in testing, through the subscribers lines if he is calling, and through the supervisory relay of the other connecting cord, to the positive side of battery if he is being called, and through both after he has re sponded. This we shall claim in broad terms.

With respect to our test circuit hereinafter described and claimed, it is to be understood that while the terms of the claims specify a subscribers line, we mean this to include any line having multiple-jacks, and requiring to be tested before being put into use as part of a subscribers or other circuit.

It will be understood that in the following specification, the system in all its parts is decribed to complete an operative whole, but our signal and test circuits might be used in other systems, and this particular system of central office apparatus and circuits is elsewhere claimed by us, as above stated.

Other features of our invention will appear hereafter from the description and claims.

In the accompanying drawing, wherein similar parts are pointed out by the same letters throughout, the figure is a diagram illustrating our invention.

In the drawing, A and B represent two subscribers stations each connected to the central ofiice, C, by line-wires 1 and 2. As these stations are alike in their equipment and connections, we will describe the station A for both. At this station, the line-wires 1 and 2 are normally connected for alternating currents through the condenser P, ringer Q, and switch-hook H, the hook being down. When the receiver is removed from the hook, the bell or ringer circuit is broken, and the talking circuit is completed through the transmitter T and the receiver B.

At the central office the main battery B is connected between bus-bars 38 and 39. The line-wire 1 is connected to the bus-bar 39 through the choke coil 8, and wires 27 and 28. Line-wire 2 is connected tothe bus-bar 38 through the line relay winding 9, the choke coil 7 and wires 15 and 30. Line-wires 1 and 2 terminate respectively in j ack-springs 3 and 4 of the spring-jack J. A test-ring or ,thimble 6 is also provided in the jack, and

this is connected as shown to the same thimble in all the multiple-jacks of the same line, and by stems 5 and wire 29 to a point x intermediate the line relay 9 and the choke coil 7. The spring 4 is so positioned with regard to the thimble 6 that when a plug is inserted the sleeve thereof will cross the spring and thimble together. The purpose of this will be pointed out later.

The resistance of the coil 8 we usually make about 200 ohms, that of the relay 9 we make 300 ohms, and that of the coil ,7 we make 200 ohms. The relay 9 controls an armature 24, which closes on a contact point 25, connected by wire 26 to the bus-bar 39. The armature, or its equivalent, which may be a twin contact to 25, is connected by wire 16 to the line signal lamp 10, and thence by wire 17 to the other side of battery at busbar 38. It will be understood that these wire connections are not necessarily carried individually to the power board, but that common wires may form continuations of the bus-bars.

The multiple-jacks, represented by J are in every respect duplicate of the jack J, and are connected in parallel therewith to the wires 1, 2, and 29.

Interconnection of the lines for conversation is effected through the cord circuit 18- 19, 23-23. This cord circuit terminates in plugs M M, and is conductively divided, but inductively completed by the condensers 13 and 14. For continuous currents, therefore, a complete conversation circuit consists of two independent sections, which are fed separately. Each plug, M or M is provided with a tip contact 20, connected to one side,

18 or 19, of the cord, and with a sleeve contact 21, connected with the other side, 23, of the cord.

For each cord circuit two supervisory relays, R R, are provided. We will describe the one B for both. This consists in the present case of a horse-shoe permanent magnet, 11, having windings upon its two poles of approximately 750 ohms resistance, connected by wires 22 and 34 to the cord conductor 23 on one side and to bus-bar 340 on the other. This bus-bar 340 is a third bus of the main battery, being connected thereto at such a point that the difierence of potential between it and the bus 38 will be much less than that between it and bus 39 the former being for instance 6 volts, and the latter 34 volts, where the total voltage of the main battery is 40. All the supervisory relays are connected to this third bus-bar. Its purpose will be referred to in the statement of operation.

Pivoted to swing between the poles of the permanent magnet 11 is an armature 36, which forms one terminal of a normally open circuit 35, whose connection is to the main bus-bar 39, and whose continuation 33 passes from bus 38 to a. lamp 12 and so by wire 32 to the contact point 31, which lies in the path of the'armature 36. A spring 37 gives the armature a normal bias to the right.

The operation of the system so described is as follows: The subscriber A we will suppose wishes to converse 'with subscriber B, He removes the receiver R from the hook H, which thereupon rises and closes the circuit through the talking set and permits direct current from the main battery to pass through the following circuit: bus-bar 39, wire 27, choke coil 8, wire 28, line-wire 1, talking set R, T, H, linewire 2, wire 15, relay 9, choke coil 7, wire 30, to busbar 38. This energizes the relay 9, which thereupon attracts its armature 24, and closes the local line-lamp circuit as follows: bus-bar 39, wire 26, point 25, armature 24, wire 16, lamp 10, wire 17, to bus-bar 38. The lamp 10 then lights, informing the operator of the call. She responds by inserting the answering plug by the insertion of which three results are produced, viz. the cord conductors are brought into connection with the line-wires; the relay 9 is shunted by the wire 29, stem 5, of the test-thimble, the thimble itself, 6, and the sleeve of the plug to spring 4, thus causing the relay armature to fall away and extinguish the lamp 10; and the supervisory relay is connected to the jack-thimble 6 through the sleeve conductor 23 of the cord, by the following path to battery; wire 22, cord conductor 23, plug sleeve 2], jackthimble 6, stem 5, wire 29, coil 7, wire 30, to bus 38 and battery B, through the upper division 40 of the battery to the bus 340, and by wire 34 back to the relay. This current flowing through the relay coils under an electromotive force of say six volts, if unopposed would suflice to overcome the spring 37 of the armature 36, drawing the latter over to the left and closing on the contact 31, thus lighting the lamp 12 by current flowing in circuit 39, 35, 36, 31, 32, 12, 33, 38 to battery. The lighting of the lamp in answering the call is prevented, however, by an opposing current that flows in the following circuit: bus-bar 39, wire 27, coil 8, wire 28, line-wire 1, subscribers talking set (which is in service) line-wire 2, spring 4, sleeve or thimble 6, sleeve or plug 21, wire 23, wire 22, windings of relay 11, wire 34 to bus-bar 340 and so to battery. We thus have a divided battery connected so that there are opposed electromotive forces through the windings of the relay R, and as they are unequal the resultant current is in a direction to reinforce the spring 37, and not to oppose it. Thus the supervisory lamp does not light for the calling line. Having ascertained the number wanted, the operator proceeds to test to determine if the wanted line is free. This she does by throwing over the listening key K to listening position and thereby bringing her head phone into connection with the tip of the calling plug M on one side, by the path 51, K, 52, 19 and 20; and into connection with the bus-bar 39 of the main battery on the other side, by the path 53, choke coil 54, 55, to bus 38. Now when the tip 20 is touched to the thimble 6 of the wanted line, if the subscriber has made a call from station B and has not yet been answered a circuit will be completed from the tip through the thimble 6, to line and back, and by conductor 28, coil 8, and wire 27 to the bus bar 39, the current flowing in this circuit producing a characteristic busy click in the operators car. If another operator has made connection with the subscribers line, but he has not yet answered the call, then a click will be obtained by current in a circuit through the thimble 6 to the corresponding thimble of the multiple jack already in use, and over the sleeve of the plug therein and its cord conductor 23 to the polarized relay R and to bus-bar340. If a cord at another section has already been brought into connection with the wanted subscribers line, and he has already answered the call then both the paths traced will be available for current to produce the click. it the line is idle, however, no click will be obtained, because the tip 20 and sleeve or thimble 6 will be at the same potential.

It will be observed that connection is made to but one side of the cord from the battery B, and a word of explanation is here in. place concerning the current supply for talking. The battery has the permanent branches 27 and 30, including the choke coils S and 7 respectively, by which direct current is fed to the lines in parallel, the choke coils preventing any propagation of the changes due to speech in the battery bridge but forcing all speech currents to go across through the cord from line to line, past the battery branches. The branch 2234 through the supervisory relays is for the purpose of supplying current to said relays, but incidentally it also carries part of the line supply.

Having thus described our invention, what we claim and desire to secure by Letters Patent of the United States is:

The combination with a multiple switchboard telephone line, a pair of line conductors, a battery permanently connected between the line conductors, a plurality of testing terminals connected with one line conductor, the portion of said line conductor between the testing terminals and the battery having an appreciable resistance whereby when a subscriber calls and connects the two line conductors together the testing terininals have their potential raised and the line is placed in condition to test busy, an operators cord and plug testing terminal to cooperate with any of the before-mentioned testing terminals, a line relay and means to short circuit the same by the insertion of the plug, and a polarized supervisory relay connected from the cord to an intermediate point on the battery whereby the opening of the line by the subscriber will reverse the potential of the said relay simultaneously with lowering of the test potential.

In witness whereof we have hereunto set our hands in the presence of two witnesses this 9th day of Feby. A. D. 1903.

JACOB 1V. LATTIG. CHARLES LANE GOODRUM.

\Vitnesses:

H. G. DESIIUNT, T. S. MITCHELL.

LOO 

